This invention relates generally to a gripper device such as used in a robotic arm and more particularly provides for improved operation in a robotic arm by detecting and controlling the grasping force of a pick-up hand attached thereto.
Robotics has become an integral part of an ever increasing number of industrial applications. Robotic systems including automatically controlled arm and hand combinations for grasping, manipulating and moving an object are now even available in nonindustrial applications such as in performing ordinary household tasks. The operating capabilities of such systems depend upon the electromechanical complexity of the robotic system itself. For example, the number of degrees of freedom of the robot arm determines the number of control parameters to be generated and regulated.
In general, a robotic hand includes two linearly displaceable, facing elements for engaging an object to be manipulated. The robotic hand may be capable of continuous operation from full open to full closed positions in order to grasp objects of various sizes or it may be limited to an intermediate position so as to accommodate only objects of a predetermined size. In general, limit switches are used for controlling the positions of the grasping element in such applications. In addition, a limit may be imposed upon the grasping force of the hand mechanism to permit the manipulation of objects of various sizes without breakage or damage thereto.
One approach to detecting the magnitude of the grasping force makes use of compressible conductive foam, the resistance of which is a function of the applied pressure. The manner in which the grasping force is controlled, of course, depends upon the environment in which the robotic arm is to be employed, with the aforementioned capability for accommodating objects of various sizes generally representing the more challenging, complicated and expensive robotic control system. An example of such a control unit for an industrial robot can be found in U.S. Pat. No. 4,240,016 to Inaba et al which makes use of a plurality of detectors for detecting the position of a robotic arm in terms of its several degrees of freedom and a single velocity unit which, under the control of a central processing unit, is connected to one of the axis position control units and one of the motors in accordance with an axis selecting instruction read out from the memory. To date, such systems have been overly complicated such that their use has generally been limited to sophisticated industrial applications.
The present invention is intended to overcome the aforementioned limitations of the prior art by providing an inexpensive and flexible arrangement for measuring and controlling the grasping force applied by a gripper device in a robotic arm upon a manipulated object.